Greeeen (stylized as GReeeeN) is a Japanese pop rock/hip hop/breakbeat vocal group from Kōriyama in Fukushima Prefecture, comprising the all-male four members Hide, Navi, Kuni (written as "92"), and Soh. They made their debut with Universal Music in 2007. Their logo image is of a mouthful of teeth, and the four Es indicate the number of members. The sound production is handled by Hide's older brother JIN, a former guitarist of Pay money To my Pain. According to their website at Universal Music Japan, their catch phrase is "Rock 'n' Breakbeats with Four Microphones".

One notable characteristic is that none of the members have ever shown their faces in the public sphere as a part of GReeeeN, whether in their promotional videos, CDs, television performances, or the Internet. In their only performance on TV-U Fukushima's music show Music Bar Palo Palo (broadcast on January 19, 2007), the group even went as far as censoring their faces during the performance. GReeeeN cites keeping their professional lives in dentistry compatible with their musical ventures as the reason, but one of the members, Hide, has hinted that after all of the members pass the prefectural examination in dentistry and receive permission from the directors of the hospitals they work for, the group may consider a public appearance.

All members studied at the dentistry department at Ohu University in Fukushima Prefecture and the group debuted while still in school in 2007.

The members' identities are still unknown, as their faces have never been made public. At first, the group stated that they would wait until all of the members passed the exam before revealing their faces, but in 2009 they indicated that they will still keep their identities secret to avoid any interference with their careers as dentists.